In their seminal work, Östh et al. [1]} further enhanced the closure theory emphasizing the modal eddy viscosity concept. The roots of such mode-dependent correction go back to the work of Rempfer and Fasel [2]} in order to provide improved closure models.
These multi-modal closures can be specified as
\(\tilde{\mathfrak {L}}^{i}_{k} = \bigg (\eta _k \frac{\partial ^2 \psi _i(x) }{\partial x^2}, \psi _{k}(x) \bigg ). \) 
